A feeding device of this kind is known from DE 30 32 971 C. This known feeding device is operated alternatingly together with at least one further similar feeding device. The feeding device, in particular, is a so-called measuring feeding device apt to measure the length of the yarn inserted during a pick. For this purpose four radially oriented, pin-shaped stop elements provided in the storage body are coupled to a planetary gear. The planetary gear is driven from the drive shaft of the winding element and displaces each stop element from a position close to the winding element and radially distant from the storage surface, to a position in front of a just forming winding of the yarn exiting from the winding element, and then in the axial direction into the stop position in which the withdrawn yarn is caught at the stop element. Subsequently, the stop element again is displaced in the radial direction and away from the windings. The stop element functions as a conveying element for the windings on the storage body and terminates the respective pick. Since the stop element is not able to start the pick, a controlled yarn clamp is provided downstream which clamps the yarn while the stop element is displaced away from the windings. The opening movement of the yarn clamp into the passive position then starts the pick. As each stop element moves only relatively slowly with the power drive and as the power drive needs a lot. of space, the storage body has to have an undesirably large diameter (strong ballooning effect). To achieve a high pick frequency, at least one further, similar feeding device is needed which operates in alternation. The mechanical load for the yarn is high. The mechanical load and the strong ballooning effect caused by the large diameter of the storage body tend to cause frequent yarn breakages or pick faults and lead to insertion delays in case of high yarn withdrawal speed.
A similar feeding device is known from EP0 250 359 A. Each stop element is one tooth of a gear wheel. Each tooth gradually is pushed between the windings on the storage surface as a consequence of the driving motion of the gear wheel derived from the driving shaft of the winding element, and is then conveyed forwards together with the windings before the tooth terminates the pick in the stop position. The yarn clamp needed for starting the pick is provided at the storage body. Due to the slow movement of each stop element in the feeding device and because of the large mounting space of the drive in the feeding device, a storage body having a relatively large diameter is needed for elevated pick speeds. The large diameter leads to an undesirably strong ballooning effect (high mechanical load in the yarn and considerable pick flight time delays).
It is an object of the invention to provide a feeding device as mentioned in the introduction which can be used for high pick frequencies and high pick speeds, even in case of delicate yarn material, which operates substantially without disturbances and which achieves optimally short insertion times.
Said object is achieved by providing a small diameter storage body, and a stop element which in its engagement position is moved axially into the stop position exclusively by the windings and the conveying motion of the windings.
The combination of a small diameter storage body and a stop element which axially is moved into the stop position exclusively by the advancing motion of the windings allows utilization of the yarn feeding device substantially without disturbances, even in the case of high pick frequencies and/or high pick speeds and even with delicate yarn material. The small diameter storage body significantly reduces the ballooning effect or the kinetic energy intermediately stored in a yarn balloon, respectively, such that very high insertion speeds, and in particular short insertion times, can be achieved without excessive mechanical load for the yarn. The small diameter storage body, however, needs a large number of windings for each pick. Mechanical disturbances of the movements of the windings on the storage body by the stop element should be avoided. This prerequisite is fulfilled when the stop element is moved exclusively axially into the stop position by the windings. The stop element does not need a drive for this movement. The stop element is taken along with the windings and follows the advancing movements of the windings with minimum or even no mechanical resistance, which advancing movement of the windings is generated in a suitable way by the winding process, i.e. the stop element is dragged by the windings. Since the axial movement of the stop element into the stop position does not need any control from outside or from inside, the drive of the stop element only has to control the precise engagement of the stop element between the windings and to release disengagement again later substantially in the radial direction. In the combination, these features result in a synergy effect leading to high operational reliability even in the case of high yarn speed and/or short pick times and/or high pick frequencies. A small diameter storage body means a storage body which has a significantly smaller outer diameter in contradiction to the conventional tendency of feeding devices having a yarn length measuring function. In feeding devices having a yarn length measuring function, a large storage body is provided to have as few windings as possible on the storage body for each pick and also to have only an axial short yarn supply on the storage body.
A conventional controlled yarn clamp may, under certain conditions, not be good enough to cope with high pick speeds and to precisely start the pick in adaptation to the weaving machine cycle. For this reason, the yarn clamp is equipped with a quick opening mechanism to assist in the positive effects of the small diameter storage body and of the stop element which is moved only by the windings into the stop position. The yarn clamp in this case is able to start the pick at a precisely predetermined point in time and particularly rapidly, e.g. within only a few milliseconds or even in a shorter period of time.
Expediently, the small outer diameter of the storage body defines a curvature of the circumference of the storage surface which at least substantially corresponds with the natural capability of natural, synthetic or compound yarn material to store a smallest unforced curvature. The yarn windings will lie relatively powerless, relaxed and in good order on the storage body. The rapid withdrawal of the yarn from this very small outer diameter storage body then only leads to a minimum ballooning effect. The result of the natural capability of the yarn to store a smallest unforced curvature means a certain bent yarn found when a free yarn section first is bent on a smooth surface to a very small loop and is then released. This loop expands somewhat but maintains then a residual curvature. This residual curvature is used as a guideline for dimensioning the outer diameter of the storage body. Astonishingly, it has been found that different yarn qualities and different yarn materials with very few exceptions develop very similar unforced residual curvatures and for that reason can be processed well on the small diameter storage body.
In case of an outer diameter between about 25 mm to 55 mm, preferably, and even in case of an outer diameter about only 35 mm to 40 mm, the ballooning effect even in the case of high pick speed is desirably weak. (The centrifugal force in the yarn is about proportional to the square of the radius of the curvature.) The small diameter allows astonishingly short insertion times even with moderate energy input, because the yarn is very willing to be withdrawn easily. The small diameter storage body may even be expedient for feeding devices for projectile or rapier weaving machines, e.g. in co-action with a withdrawal brake co-operating with the small diameter storage body. In such a case the stop element and the yarn clamp may be omitted.
The outer diameter may be so small that the axial length of the storage surface is substantially larger than the outer diameter.
Expediently, the stop element is connected by a hinge with a radial adjustment drive provided axially stationarily. The radial adjustment drive adjusts the stop element in a precisely timed manner and reliably into engagement in front of the just arriving yarn winding exiting from the winding element. The hinge or the bending section offers the necessary degree of freedom for the stop element thanks to which the stop element will be brought into the stop position only by the advance movement of the windings on the storage body substantially without any counter force.
In order to axially return the stop element in front of the first formed winding to prepare for the next yarn length measuring function, an axial adjustment drive is employed which returns the stop element which moves about the hinge or the bending section and after the stop element first has been brought radially into the release position. Alternatively, even several sequentially operating stop elements may be employed instead.
In the stop position the stop element is caught at an axial stop. This stop may be provided in the storage body or even radially outside of the storage body.
Catching the yarn in the stop position of the stop element causes the undesirable stretching effect or whiplash effect due to the momentary deceleration of the mass of the yarn. As a counter measure it is particularly expedient to associate an impact damper to the stop element in the stop position for alleviating/moderating the stretching effect or the whiplash effect. That measure reduces the danger of a yarn breakage considerably. The impact damper dissipates energy by resiliently giving way. The energy meant is introduced by the decelerated yarn into the stop element. The stop for the stop element may move e.g. counter to a spring force over a small travelling stroke either in the axial direction, in an inclined direction or in a circumferential direction of the storage body, respectively, in order to dissipate the energy. The stop element even may be elastically deformable in itself in order to carry out the impact damping effect as soon as the yarn is stopped abruptly when the stop element has reached the stop.
In order to precisely control and predetermine the point in time of the start of the pick by the yarn clamp, it is expedient to open the yarn clamp by an actuating solenoid and to provide for the armature of the actuating solenoid a certain idle stroke in relation to the clamping element of the yarn clamp. As soon as the actuating solenoid is excited, the armature uses the idle stroke to first accelerate free from the mass of the clamping element and the oppositely directed spring force, and first to build up a lot of kinetic energy during the acceleration, and then to displace the clamping element abruptly into the passive position after the idle stroke has been passed with high acceleration and/or high kinetic energy. In this way a yarn clamp opening time may be reached which is in the range of only a few milliseconds or even shorter.
In view of a precise yarn control in the operational phase in which the stop element is brought from the stop position into the release position, it may be expedient to move the yarn clamp which clamps the yarn substantially opposite to the withdrawal direction of the yarn towards the storage body. For this purpose a displacement drive is used, e.g. a stepper motor, which shifts or pivots the yarn clamp. By moving the yarn clamp while holding the yarn closer to the storage body the yarn section between the yarn clamp and the stop element placed in the stop position will be relaxed such that no significant stretching tension will be present in this yarn section when the stop element finally is displaced substantially radially out of the stop position. Such a yarn stretching tension, otherwise, would result in an abrupt relaxation during the movement of the stop element causing a disorder in the yarn windings on the storage body. First, after the stop element has been brought into the release position and/or after the yarn clamp has been brought into the passive position, the yarn clamp again is returned in the opposite direction.
Although the ballooning effect can be ignored in case of such a small storage body, the yarn may carry out a rotating movement in the final phase of the pick and within a movement space in which it might get caught by the yarn clamp or in the clamping section of the yarn clamp. For this reason the yarn clamp should be removable out of this moving area.